This invention relates to a valve for an aerosol container with the aid of which a quantity of the contents thereof can be dispensed. The invention has particular application to the dispensing of metered doses of medicaments, though it is applicable to the dispensing of aerosols generally.
The continuing use of aerosol formulations comprising conventional chlorofluorocarbon propellants is being debated due to the suspected role of such propellants in atmospheric depletion of ozone. Accordingly, formulations based on alternative propellants such as HFA-134a (1,1,1,2-tetrafluoroethane) and HFA-227 (1,1,1,2,3,3,3-heptafluoropropane) are being developed to replace those conventional propellants thought to contribute to atmospheric ozone depletion.
Containers for aerosol formulations commonly comprise a vial body coupled to a valve. The valve comprises a valve stem through which the formulations is dispensed. Generally the valve includes a rubber valve seal intended to allow reciprocal movement of the valve stem while preventing leakage of propellant from the container.
It has been found that some conventional devices for delivering aerosols suffer impaired performance when used in connection with HFA-134a or HFA-227.
Selection of suitable materials for use in valves to contain aerosol formulations based on these alternative propellants is complicated by interactions between the valve component materials and the formulation components, including the propellant. In conventional devices, particularly with some drug formulations the valve stem tends to stick, pause, or drag during the actuation cycle with the result that the user perceives a xe2x80x98notchinessxe2x80x99 as the valve stem is depressed and released. This may be partly caused by the drug to be dispensed from the container sedimenting or precipitating out of the drug-propellant suspension or solution formulation and depositing on the internal valve components, the presence of drug on the sliding interface creating increased friction during operation.
International Patent Application No. PCT/US94/06900 describes an aerosol valve wherein the rubber valve seal is made of a composition specially selected to minimise leakage of the propellant through the interface between the valve seal and valve stem upon firing. Smoothness of operation is also improved with some formulations compared to devices involving conventional thermoset rubber seals. However, although such seal compositions may improve valve performance, they do not prevent build up of deposit on the valve components, and the problem of notchiness may persist.
It is an object to provide a valve with improved smoothness of operation which alleviates the problem of valve sticking.
According to one aspect of the present invention there is provided a valve for an aerosol container for dispensing a suspension of a substance in a liquid propellant contained therein, the valve comprising a valve body defining an aperture, a seal mounted at the aperture, and a valve stem having a dispensing passage, the valve stem being slideably moveable through the seal such that in a first position the valve is closed to prevent the substance to be dispensed from entering the dispensing passage, and in a second position the valve is open to allow the substance to be dispensed through the dispensing passage, characterised in that the valve stem is made from a material comprising lubricant.
According to another aspect of the present invention there is provided a valve stem made from a material comprising lubricant. According to a further aspect of the present invention there is provided an aerosol container comprising a valve as described herein.
Incorporating lubricant into the material of the valve stem ensures that the lubricant is comprised within the maximum area of the stem/seal contact surface, so providing improved lubrication and smoothness of operation for the life of the valve. The term xe2x80x98lubricantxe2x80x99 means any material which reduces friction between the valve stem and seal.
Suitably, the lubricant comprises a fluorine containing polymer such as polyetrafluoroethane (PTFE),ethylenetetrafluoroethylene (ETFE), perfluoroalkoxyalkane (PFA), fluorinated ethylene propylene (FEP), vindyidionefluoride (PUDF), and chlorinated ethylene tetrafluoroethylene. Preferably the lubricant comprises polytetrafluoroethane (PTFE). More preferably, the lubricant consists of polytetrafluoroethane (PTFE).
PTFE has been found to be particularly advantageous as a lubricant due to its low coefficient of friction. Furthermore, PTFE significantly reduces the problem of drug deposition on the valve stem, so removing one of the causes of valve sticking.
Suitably, the valve stem comprises up to 20% by weight of PTFE. Preferably, the valve stem comprises 5 to 10% by weight of PTFE.
PTFE can be plastic moulded and may be used effectively in small quantities constituting of the order of 5% by weight of the material of the valve stem. PTFE is also non-toxic, an important consideration for aerosol devices for dispensing medicaments.
In one aspect, the valve stem is free from any silicone material, such as silcone oil, either as a component thereof or coating thereon.
Suitably, the valve is a metering valve comprising a metering chamber, a transfer passage through which a quantity of substance to be dispensed can pass from the container into the metering chamber, wherein in the first position the dispensing passage is isolated from the metering chamber and the metering chamber is in communication with the container via the transfer passage, and in the second position the dispensing passage is in communication with the metering chamber and the transfer passage is isolated from the metering chamber.
Suitably the substance to be dispensed is a medicament suspended in liquefied HFA-134a or HFA-227.
Medicaments suitable for this purpose are, for example for the treatment of respiratory disorders such as asthma, bronchitis, chronic obstructive pulmonary diseases and chest infections. Additional medicaments may be selected from any other suitable drug useful in inhalation therapy and which may be presented as a suspension. Appropriate medicaments may thus be selected from, for example, analgesics, e.g. codeine, dihydromorphine, ergotamine, fentanyl or morphine; anginal preparations, e.g. diltiazem; antiallergics, e.g. cromoglycate, ketotifen or neodocromil; antiinfectives e.g. cephalosporins, penicillins, streptomycin, sulphonamides, tetracyclines and pentamidine; antihistamines, e.g. methapyrilene anti-inflammatories, e.g. fluticasone propionate, beclomethasone dipropionate, flunisolide, budesonide or triamcinolone acetonide; antitussives, e.g. noscapine; bronchodilators, e.g. salmeterol, salbutamol, ephedrine, adrenaline, fenoterol, formoterol, isoprenaline, metaproterenol, phenylephrine, phenylpropanolamine, pirbuterol, reproterol, rimiterol, terbutaline, isoetharine, tulobuterol orciprenaline, or (xe2x88x92)4-amino-3,5dichloro-xcex1[[[6-[2-(2-pyridinyl)ethoxy]-hexyl]amino]methyl] benzenemethanol; diuretics, e.g. amiloride; anticholinergics e.g. ipratropium, atropine or oxitropium; hormones, e,g, cortisone, hydrocortisone or prednisolone; xanthines e.g. aminophylline, choline theophyllinate, lysine theophyllinate or theophylline and therapeutic proteins and peptides, e.g. insulin or glucagon. It will be clear to a person skilled in the art that, where appropriate, the medicaments may be used in the form of salts (e.g. as alkali metal or amine salts or as acid addition salts) or as esters (e.g. lower alkyl esters) or as solvates (e.g. hydrates) to optimise the activity and or stability of the medicament. Preferred medicaments are salbutamol, salbutamol sulphate, salmeterol, salmeterol xinafoate, fluticasone propionate, beclomethasone dipropionate and terbutaline sulphate. It is to be understood that the suspension or solution of medicament may consist purely of one or more active ingredients.
Preferably the medicament is salmeterol xinafoate, fluticasone propionate or a combination thereof .